Paclitaxel-Loaded Expansile Nanoparticles in a Multimodal Treatment Model of Malignant Mesothelioma

Drug Delivery Opportunities in Esophageal Cancer: Current Treatments and Future Prospects

With one of the highest mortality rates of all malignancies, the 5-year survival rate for esophageal cancer is under 20%. Depending on the stage and extent of the disease, the current standard of care treatment paradigm includes chemotherapy or chemoradiotherapy followed by surgical esophagogastrectomy, with consideration for adjuvant immunotherapy for residual disease. This regimen has high morbidity, due to anatomic changes inherent in surgery, the acuity of surgical complications, and off-target effects of systemic chemotherapy and immunotherapy. We begin with a review of current treatments, then discuss new and emerging targets for therapies and advanced drug delivery systems. Recent and ongoing preclinical and early clinical studies are evaluating traditional tumor targets (e.g., human epidermal growth factor receptor 2), as well as promising new targets such as Yes-associated protein 1 or mammalian target of rapamycin to develop new treatments for this disease. Due the function and location of the esophagus, opportunities also exist to pair these treatments with a drug delivery strategy to increase tumor targeting, bioavailability, and intratumor concentrations, with the two most common delivery platforms being stents and nanoparticles. Finally, early results with antibody drug conjugates and chimeric antigenic receptor T cells show promise as upcoming therapies. This review discusses these innovations in therapeutics and drug delivery in the context of their successes and failures, with the goal of identifying those solutions that demonstrate the most promise to shift the paradigm in treating this deadly disease.

Radiolabeled Biodistribution of Expansile Nanoparticles: Intraperitoneal Administration Results in Tumor Specific Accumulation

Nanoparticle biodistribution in vivo is an essential component to the success of nanoparticle-based drug delivery systems. Previous studies with fluorescently labeled expansile nanoparticles, or "eNPs", demonstrated a high specificity of eNPs to tumors that is achieved through a materials-based targeting strategy. However, fluorescent labeling techniques are primarily qualitative in nature and the gold-standard for quantitative evaluation of biodistribution is through radiolabeling. In this manuscript, we synthesize 14C-labeled eNPs to quantitatively evaluate the biodistribution of these particles in a murine model of intraperitoneal mesothelioma via liquid scintillation counting. The results demonstrate a strong specificity of eNPs for tumors that lasts one to 2 weeks postinjection with an overall delivery efficiency to the tumor tissue of 30% of the injected dose which is congruent with prior reports of preclinical efficacy of the technology. Importantly, the route of administration is essential to the eNP's material-based targeting strategy with intraperitoneal administration leading to tumoral accumulation while, in contrast, intravenous administration leads to rapid clearance via the reticuloendothelial system and low tumoral accumulation. A comparison against nanoparticle delivery systems published over the past decade shows that the 30% tumoral delivery efficiency of the eNP is significantly higher than the 0.7% median delivery efficiency of other systems with sufficient quantitative data to define this metric. These results lay a foundation for targeting intraperitoneal tumors and encourage efforts to explore alternative, nonintravenous routes, of delivery to accelerate the translation of nanoparticle therapies to the clinic.

Ultra-high drug loading improves nanoparticle efficacy against peritoneal mesothelioma

Peritoneal mesothelioma is an aggressive disease with a median survival of under three years, due to a lack of effective treatment options. Mesothelioma is traditionally considered a "chemoresistant" tumor; however, low intratumoral drug levels coupled with the inability to administer high systemic doses suggests that therapeutic resistance may be due to poor drug delivery rather than inherent biology. While patient survival may improve with repetitive local intraperitoneal infusions of chemotherapy throughout the perioperative period, these regimens carry associated toxicities and significant peri-operative morbidity. To circumvent these issues, we describe ultra-high drug loaded nanoparticles (NPs) composed of a unique poly(1,2-glycerol carbonate)-graft-succinate-paclitaxel (PGC-PTX + PTX) conjugate. PGC-PTX + PTX NPs are cytotoxic, localize to tumor in vivo, and improve survival in a murine model of human peritoneal mesothelioma after a single intraperitoneal (IP) injection compared to multiple weekly doses of the clinically utilized formulation PTX-C/E. Given their unique pharmacokinetics, a second intraperitoneal dose of PGC-PTX + PTX NPs one month later more than doubles the overall survival compared to the clinical control (122 versus 58 days). These results validate the clinical potential of prolonged local paclitaxel to treat intracavitary malignancies such as mesothelioma using a tailored polymer-mediated nanoparticle formulation.

Local Therapies and Modulation of Tumor Surrounding Stroma in Malignant Pleural Mesothelioma: A Translational Approach

Malignant Pleural Mesothelioma (MPM) is a rare and aggressive neoplasm of the pleural mesothelium, mainly associated with asbestos exposure and still lacking effective therapies. Modern targeted biological strategies that have revolutionized the therapy of other solid tumors have not had success so far in the MPM. Combination immunotherapy might achieve better results over chemotherapy alone, but there is still a need for more effective therapeutic approaches. Based on the peculiar disease features of MPM, several strategies for local therapeutic delivery have been developed over the past years. The common rationale of these approaches is: (i) to reduce the risk of drug inactivation before reaching the target tumor cells; (ii) to increase the concentration of active drugs in the tumor micro-environment and their bioavailability; (iii) to reduce toxic effects on normal, non-transformed cells, because of much lower drug doses than those used for systemic chemotherapy. The complex interactions between drugs and the local immune-inflammatory micro-environment modulate the subsequent clinical response. In this perspective, the main interest is currently addressed to the development of local drug delivery platforms, both cell therapy and engineered nanotools. We here propose a review aimed at deep investigation of the biologic effects of the current local therapies for MPM, including cell therapies, and the mechanisms of interaction with the tumor micro-environment.

Paclitaxel-loaded expansile nanoparticles improve survival following cytoreductive surgery in pleural mesothelioma xenografts

OBJECTIVE

Malignant pleural mesothelioma is a lethal malignancy with poor survival and high local recurrence rates despite multimodal therapy with cytoreduction and chemoradiation. We evaluated the antitumor efficacy of a paclitaxel-loaded pH-responsive expansile nanoparticle (PTX-eNP) in 2 clinically relevant murine xenograft models of malignant pleural mesothelioma.

METHODS

Luciferase-transfected MSTO-211H human mesothelioma cells were injected into the thoracic cavity of immunodeficient Nu/J mice. Tumor burden was monitored by bioluminescent imaging. Animals were randomized into 2 models of disease treatment chemotherapy with PTX-eNPs alone delivered locally for early limited disease or cytoreductive surgery plus local PTX-eNP chemotherapy for advanced disease. Within each disease model, anti-tumor efficacy of PTX-eNP was compared against standard formulation paclitaxel and drug-empty nanoparticles. Influence on survival was calculated. Fluorescently labeled PTX-eNPs and immunohistochemistry evaluated in vivo drug localization to tumor.

RESULTS

Intrathoracic injection of MSTO-211H resulted in large tumor deposits distributed within the pleural space of the murine thoracic cavity. Local multidose treatment with PTX-eNPs alone in limited stage disease more than doubled survival compared with drug-empty nanoparticles (P ≤ .0001) and standard formulation paclitaxel (P = .0004). In the model of advanced disease, local multidose treatment with PTX-eNPs following cytoreductive surgery also prolonged survival by 126% and 69.4% compared with drug-empty nanoparticles (P = .0018) and standard formulation paclitaxel (P = .03457), respectively. Immunohistology demonstrated PTX-eNP accumulation within tumor cells in vitro and in vivo.

CONCLUSIONS

Local delivery of paclitaxel via eNPs confers prolonged survival in a murine model of malignant pleural mesothelioma as single modality treatment for limited disease and in combination with cytoreductive surgery for advanced disease.

Expansile Nanoparticles Encapsulate Factor Quinolinone Inhibitor 1 and Accumulate in Murine Liver upon Intravenous Administration

Expansile nanoparticles (eNPs) are a promising pH-responsive polymeric drug delivery vehicle, as demonstrated in multiple intraperitoneal cancer models. However, previous delivery routes were limited to intraperitoneal injection and to a single agent, paclitaxel. In this study, we preliminarily evaluate the biodistribution and in vivo toxicity of eNPs in mice after intravenous injection. The eNPs localize predominantly to the liver, without detectable acute toxicity in the liver or other key organs. On the basis of these results, we encapsulated FQI1, a promising lead compound for treatment of hepatocellular carcinoma, in eNPs. eNPs are taken up by cancerous and noncancerous human liver cells in vitro, although at different rates. FQI1-loaded eNPs release FQI1 in a pH-dependent manner and limit proliferation equivalently to unencapsulated FQI1 in immortalized hepatocytes in vitro. eNPs are a versatile platform delivery system for therapeutic compounds and have potential utility in the treatment of liver disease.

Management of recurrence after initial surgery for malignant pleural mesothelioma: a mini-review

Recurrence after surgery in the multimodality therapy for malignant pleural mesothelioma is a common problem. As the majority of patients experience not only local but also distant metastases, a systemic treatment strategy in addition to local control measures remains necessary. Nevertheless, none of the chemotherapy regimens have achieved clinical success. Local management modalities such as stereotaxic treatments, cryoablation and redo surgery on the other hand have promising results, but provide palliative outcomes.

Two-Step Delivery: Exploiting the Partition Coefficient Concept to Increase Intratumoral Paclitaxel Concentrations In vivo Using Responsive Nanoparticles

Drug dose, high local target tissue concentration, and prolonged duration of exposure are essential criteria in achieving optimal drug performance. However, systemically delivered drugs often fail to effectively address these factors with only fractions of the injected dose reaching the target tissue. This is especially evident in the treatment of peritoneal cancers, including mesothelioma, ovarian, and pancreatic cancer, which regularly employ regimens of intravenous and/or intraperitoneal chemotherapy (e.g., gemcitabine, cisplatin, pemetrexed, and paclitaxel) with limited results. Here, we show that a “two-step” nanoparticle (NP) delivery system may address this limitation. This two-step approach involves the separate administration of NP and drug where, first, the NP localizes to tumor. Second, subsequent administration of drug then rapidly concentrates into the NP already stationed within the target tissue. This two-step method results in a greater than 5-fold increase in intratumoral drug concentrations compared to conventional “drug-alone” administration. These results suggest that this unique two-step delivery may provide a novel method for increasing drug concentrations in target tissues.

Synthesis and Characterization of Hybrid Polymer/Lipid Expansile Nanoparticles: Imparting Surface Functionality for Targeting and Stability

The size, drug loading, drug release kinetics, localization, biodistribution, and stability of a given polymeric nanoparticle (NP) system depend on the composition of the NP core as well as its surface properties. In this study, novel, pH-responsive, and lipid-coated NPs, which expand in size from a diameter of approximately 100 to 1000 nm in the presence of a mildly acidic pH environment, are synthesized and characterized. Specifically, a combined miniemulsion and free-radical polymerization method is used to prepare the NPs in the presence of PEGylated lipids. These PEGylated-lipid expansile NPs (PEG-L-eNPs) combine the swelling behavior of the polymeric core of expansile NPs with the improved colloidal stability and surface functionality of PEGylated liposomes. The surface functionality of PEG-L-eNPs allows for the incorporation of folic acid (FA) and folate receptor-targeting. The resulting hybrid polymer/lipid nanocarriers, FA-PEG-L-eNPs, exhibit greater in vitro uptake and potency when loaded with paclitaxel compared to nontargeted PEG-L-eNPs.

In vitro activity of Paclitaxel-loaded polymeric expansile nanoparticles in breast cancer cells

Through a series of in vitro studies, the essential steps for intracellular drug delivery of paclitaxel using a pH-responsive nanoparticle system have been investigated in breast cancer cells. We successfully encapsulated paclitaxel within polymeric expansile nanoparticles (Pax-eNPs) at 5% loading via a miniemulsion polymerization procedure. Fluorescently tagged eNPs were readily taken up by MDA-MB-231 breast cancer cells grown in culture as confirmed by confocal microscopy and flow cytometry. The ability of the encapsulated paclitaxel to reach the cytoplasm was also observed using confocal microscopy and fluorescently labeled paclitaxel. Pax-eNPs were shown to be efficacious against three in vitro human breast adenocarcinoma cell lines (MDA-MB-231, MCF-7, and SK-BR-3) as well as cells isolated from the pleural effusions of two different breast cancer patients. Lastly, macropinocytosis was identified as the major cellular pathway responsible for eNP uptake, as confirmed using temperature-sensitive metabolic reduction, pharmacologic inhibitors, and fluid-phase marker colocalization.

Microscopy and tunable resistive pulse sensing characterization of the swelling of pH-responsive, polymeric expansile nanoparticles

Polymeric expansile nanoparticles (eNPs) that respond to a mildly acidic environment by swelling with water and expanding 2-10× in diameter represent a new responsive drug delivery system. Here, we use a variety of techniques to characterize the pH- and time-dependence of eNP swelling as this is a key property responsible for the observed in vitro and in vivo performance of eNPs. Results demonstrate a significant change in eNP volume (>350×) at pH 5.0 as seen using: scanning electron microscopy (SEM), conventional transmission electron microscopy (TEM), freeze-fracture transmission electron microscopy (ff-TEM), fluorescence microscopy, and a new nanopore based characterization technology, the qNano, which measures both individual particle size as well as overall particle concentration in situ using tunable resistive pulse sensing. eNP swelling occurs in a continuous and yet heterogeneous manner over several days and is pH dependent.

Cytoreductive surgery and intraoperative administration of paclitaxel-loaded expansile nanoparticles delay tumor recurrence in ovarian carcinoma

BACKGROUND

Locoregional recurrence significantly impacts survival and quality of life in patients with ovarian carcinoma. We hypothesize that local administration of paclitaxel-loaded expansile nanoparticles (pax-eNP) at the time of cytoreductive surgery decreases local tumor recurrence.

METHODS

In vitro cytotoxicity of pax-eNP was assessed against both the OVCAR-3 human ovarian cancer cell line and tumor cells isolated from a malignant pleural effusion from a patient with multidrug-resistant ovarian cancer. A murine xenogenic model involving surgical cytoreduction of established OVCAR-3 intra-abdominal tumor was used to evaluate in vivo efficacy of intraoperative intraperitoneal (IP) injection of 10 mg/kg of paclitaxel either as pax-eNP or paclitaxel in Cremophor EL/ethanol solution (pax-C/E) versus empty eNP controls. Cytoreductive surgery and intraoperative treatment were performed 4 weeks after established tumor. All animals were sacrificed when empty eNP controls displayed extensive evidence of disease progression.

RESULTS

Labeled-eNP entered tumor cells in vitro within 4 h and specifically accumulated at sites of tumor in vivo. Pax-eNP exhibited dose-dependent cytotoxicity in both OVCAR-3 and patient tumor cells isolated from a malignant pleural effusion and effectively prevented tumor recurrence following debulking (p = 0.003 vs. empty eNP). Furthermore, pax-eNP-treated animals did not develop severe recurrent carcinomatosis compared with 43 % of the pax-C/E-treated cohort, suggesting that single-dose intracavitary pax-eNP is more effective than an equivalent dose of pax-C/E.

CONCLUSIONS

Expansile nanoparticles readily enter human ovarian tumor cells and localize to sites of tumor in vivo with pax-eNP cytotoxicity resulting in superior inhibition of locoregional tumor recurrence following cytoreductive surgery.

Biologically responsive polymeric nanoparticles for drug delivery

Responsive nanoparticles that release their drug cargo in accordance with a change in pH or oxidative stress are of significant clinical interest as this approach offers the opportunity to link drug delivery to a specific location or disease state. This research news article reviews the current state of this field by examining a series of published articles that highlight the novelty and benefits of using responsive polymeric particles to achieve functionally-targeted drug delivery.

Molecular imaging of mesothelioma with (99m)Tc-ECG and (68)Ga-ECG

We have developed ethylenedicysteine-glucosamine (ECG) as an alternative to (18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG) for cancer imaging. ECG localizes in the nuclear components of cells via the hexosamine biosynthetic pathway. This study was to evaluate the feasibility of imaging mesothelioma with (99m)Tc-ECG and (68)Ga-ECG. ECG was synthesized from thiazolidine-4-carboxylic acid and 1,3,4,6-tetra-O-acetyl-2-amino-D-glucopyranose, followed by reduction in sodium and liquid ammonia to yield ECG (52%). ECG was chelated with (99m)Tc/tin (II) and (68)Ga/(69)Ga chloride for in vitro and in vivo studies in mesothelioma. The highest tumor uptake of (99m)Tc-ECG is 0.47 at 30 min post injection, and declined to 0.08 at 240 min post injection. Tumor uptake (%ID/g), tumor/lung, tumor/blood, and tumor/muscle count density ratios for (99m)Tc-ECG (30-240 min) were 0.47 ± 0.06 to 0.08 ± 0.01; 0.71 ± 0.07 to 0.85 ± 0.04; 0.47 ± 0.03 to 0.51 ± 0.01, and 3.49 ± 0.24 to 5.06 ± 0.25; for (68)Ga-ECG (15-60 min) were 0.70 ± 0.06 to 0.92 ± 0.08; 0.64 ± 0.05 to 1.15 ± 0.08; 0.42 ± 0.03 to 0.67 ± 0.07, and 3.84 ± 0.52 to 7.00 ± 1.42; for (18)F-FDG (30-180 min) were 1.86 ± 0.22 to 1.38 ± 0.35; 3.18 ± 0.44 to 2.92 ± 0.34, 4.19 ± 0.44 to 19.41 ± 2.05 and 5.75 ± 2.55 to 3.33 ± 0.65, respectively. Tumor could be clearly visualized with (99m)Tc-ECG and (68)Ga-ECG in mesothelioma-bearing rats. (99m)Tc-ECG and (68)Ga-ECG showed increased uptake in mesothelioma, suggesting they may be useful in diagnosing mesothelioma and also monitoring therapeutic response.

Local drug delivery strategies for cancer treatment: gels, nanoparticles, polymeric films, rods, and wafers

Polymer-based drug delivery depots have been investigated over the last several decades as a means to improve upon the lack of tumor targeting and severe systemic morbidities associated with intravenous chemotherapy treatments. These localized therapies exist in a variety of form factors designed to facilitate the delivery of drug directly to the site of disease in a controlled manner, sparing off-target tissue toxicities. Many of these depots are biodegradable and designed to maintain therapeutic concentrations of drug at the tumor site for a prolonged period of time. Thus a single implantation procedure is required, sometimes coincident with tumor excision surgery, and thereby biodegrading following complete release of the loaded active agent. Even though localized polymer depot delivery systems have been investigated, a surprisingly small subset of these technologies has demonstrated potentially curative preclinical results for cancer applications, and fewer have progressed toward commercialization. The aims of this article are to review the most well-studied and efficacious local polymer delivery systems from the last two decades, to examine the rationale for utilizing drug-eluting polymer implants in cancer patients, and to identify the patient cohorts that could most benefit from localized therapy. Finally, a discussion of the physiological barriers to localized therapy (i.e. drug penetration, transport), technical hurdles, and future outlook of the field is presented.

Hydrogels as intracellular depots for drug delivery

The intracellular activity and drug depot characteristics of micrometer-sized hydrogels are described. The hydrogel structure is formed after cellular uptake of a solid polymeric nanoparticle that swells in response to mildly acidic conditions as it transforms from a hydrophobic to a hydrophilic structure. These nanoparticles are rapidly taken up into A549 human non-small cell lung cancer cells with 88.3 ± 0.8% of cells experiencing uptake in 24 h, undergo expansion to release encapsulated drug and can effectively deliver chemotherapeutics in vitro. The anticancer drug paclitaxel was also shown to have a 3- to 4-fold increased affinity for the expanded nanoparticle state, allowing the expansile nanoparticles to act as intracellular drug depots and concentrate the drug locally.